Today, more than
80% of it comes from the burning of
fossil fuels like coal, gasoline, and natural
gas.

7

These fuels contain carbon
from decayed plants that have been
buried in the earth for millions of
years, and are now being burned so
rapidly that it has overwhelmed the
processes that naturally remove
atmospheric CO

2

.

The geographical origin of emissions
is also changing. About 80% of
CO

2

from burning fossil fuels, to date,
has come from industrialized countries
(with only 20% of the world's
population), while the remaining 80%
of the population have contributed
only 20% of the emissions.

16

Since 2000,
however, about 70% of the increase in
emissions has come from developing
countries. (Figure I).

16

Carbon dioxide is not the only
greenhouse gas related to human
activity. Methane (CH

4

, released from
industry and agriculture), nitrous
oxide (N

2

O, released mainly from
agriculture), low-atmosphere ozone
(O

3

, a by-product of smog), and several
industrial chemicals related to air
conditioning and refrigeration
together account for about 80% as
much greenhouse warming as CO

2

.

Figure III. Observed surface temperatures over continents and the globe from 1906-2005 (black line), compared with results simulated by
climate models using only natural inputs of solar activity and volcanoes (blue band; standard deviation around annual average for five
climate models, 19 simulations) and models using both natural and human inputs (pink band; standard deviation around annual average for
14 climate models, 58 simulations).